This invention pertains to back light assemblies for flat-panel displays and, more particularly, to a back light module with a single array of lamps that produces high intensity, collimated light in two directions suitable for use with large, back-to-back, tiled flat-panel displays.
Flat-panel displays (FPDs) made in accordance with known active matrix (e.g., TFT, etc.) liquid crystal display technologies (e.g., AMLCD) are typically mounted in front of a back light module which contains an array of fluorescent lamps. AMLCD flat-panel displays of this type have been increasing in size by about 1 to 2 inches diagonal, yearly. The median size in 1999 for use in desktop PCs was about 15 inches diagonal viewing area. A few very large displays are made in the range of 20 to 28 inches diagonal. Tiled AMLCD FPDs may be made in the range of 40 inches diagonal, as described in copending U.S. patent applications Ser. Nos. 09/368,921 and 09/490,776. Tiled FPDs, as described in U.S. Pat. No. 5,661,531, require extremely intense back light sources with highly collimated light, masked optical stacks, and pixel apertures that may have low emitted light efficiency. Thus, lighting with unusually high intensity ranges of 50,000 to 150,000 nits is desirable. Also, intensity uniformity over the very large areas of tiled FPDs is very important. Unique back light designs, including temperature control features, are necessary to achieve such high intensities at reasonable power consumption.
Maintaining bright (i.e., high intensity) and uniform illumination of the display over its entire active area is difficult to do. The intensity required for some applications and, in particular, that required for large, tiled, seamless flat-panel LCD displays, causes the lamps to produce a significant amount of heat. In addition, since fluorescent lamps are designed to run most efficiently at an elevated temperature, it is desirable to operate them at or near their ideal design temperature, which is usually about 50 to 60 degrees Centigrade.
Small, edge-lit back light modules, such as those used in notebook or laptop PCs, do not produce sufficient brightness for use in a large area display, nor are they capable of illuminating that large an area uniformly. Thus, it is necessary to illuminate these larger areas with an array of large fluorescent lamps. The number of lamps required depends on the size of the area to be illuminated and the display brightness requirements. A large area display generally requires multiple lamps to illuminate it properly. A large area display that can be viewed from two sides (i.e., a back-to-back display) requires proportionally more lamps, as well as unique design features to achieve the desired intensities and maintain optimized lamp efficiency through temperature control of the lamps.
Since most displays are designed to be wider than they are tall, it is advantageous, from a reliability and power perspective, to place the lamps in a horizontal orientation. This typically results in the use of fewer lamps and, consequently, lower power consumption, since fewer lamp cathodes are present. The resulting preferred designs orient lamp tubes horizontally, one above the other with predetermined, preferred spacing relationships to each other and to each of the back-to-back displays, one disposed on each side of the lamp array.
It is, therefore, a principal object of the invention to provide a back light module designed to illuminate back-to-back displays.
It is an additional object of the invention to provide a back light module for use with large flat panel displays, either monolithic or tiled.
It is another object of the invention to provide a back light module designed to provide a high intensity light output.
It is a further object of the invention to provide a back light module capable of delivering highly collimated light.
It is an additional object of the invention to provide a back light module having a very high operating efficiency.
It is a still further object of the invention to provide a back light module having a cooling structure to maintain a substantially uniform operating temperature.
It is yet another object of the invention to provide a back light module utilizing an array of horizontally-mounted fluorescent tubes.
It is an additional object of the invention to provide a back light module incorporating a cavity to maximize and control light recirculation.
It is another object of the invention to provide a back light assembly incorporating diffusers, collimators and brightness-enhancing films (BEFs).
It is a further object of the invention to provide a back light assembly suitable for illuminating large, back-to-back, tiled flat-panel displays having visually imperceptible seams.
In accordance with the present invention, there is provided a back light module which uniformly distributes luminance to back-to-back flat-panel, liquid crystal displays (LCDs) simultaneously. Fluorescent lamps are used due to their high efficiency. However, luminance, efficiency, and lamp life of fluorescent lamps are all functions of lamp tube temperature. The present invention provides an apparatus and method for achieving luminance uniformity and a high degree of light collimation in back-to-back displays with one single back light module source.
In particular, a constant and uniform luminance output of the back light module is obtained through appropriate selection of lamps, optimization of back light module geometry and use of additional optical components. A preferred balance of lamps, lamp spacing, diffuser and collimating optics is chosen to produce a high brightness back light module with very high, uniform intensity output over very large surface areas. Light is recycled from one display module to the other as the light is reflected from each of the display""s optical stacks. The optical stacks of the two display modules typically include polarizers, masks, diffusers etc. In addition, light is reflected from the light collimating optics and the light enhancing and diffusing films also typically present in the optical stacks.
This invention provides a method for achieving this goal through selection of combinations of components and appropriate design geometries. A particular application of the inventive back light module is for use in integrating two large, tiled, flat-panel displays having visually imperceptible seams as described in the aforementioned U.S. patent application Ser. Nos. 08/652,032, and 09/368,291, and U.S. Pat. No. 5,903,328. The back light module system, with thermal enhancements such as those disclosed in U.S. patent application Ser. No. 09/406,977 and applicable controls, such as those disclosed in U.S. patent application Ser. No. 09/407,619, provides for an efficient, reliable, large area, high intensity light source usable with back-to-back flat-panel displays.
Additionally, optimum geometries are determined for the purpose of maximizing light output at high efficiencies, while minimizing luminance gradients across the two displays. These optimum geometries are also determined for maximizing light output using brightness enhancing films (BEFs) and light recycling.
Finally, precise collimators such as that disclosed in U.S. patent application Ser. Nos. 09/024,481 and 60/177,447, eliminate light beyond a defined cut-off angle for each flat panel display, as required in a tiled flat-panel LCD.
It will be obvious that while the back light assembly of the invention is optimized for use with tiled, AMLCD flat-panel displays, it may also be used with monolithic and monolithic-like displays.